When producing sulphur acid problems relating to the undersirable emission of sulphur trioxide constantly occur, such occurrence being particularly evident when process equipment becomes overloaded and/or break downs in operation occur and/or production is re-started after such break downs.
Such emission can be tolerated in itself, provided that it is on such a small scale as to have no chronic effect on the environment. The emission of such gases must not be continuous, however, and consequently it is necessary to monitor gases which derive from industrial processes and which are liable to create emission problems.
Although with respect to certain gases, it is possible to assay the gas in the actual chimney stack, using light-absorption assaying methods herefor, the gas has either already been discharged from the system to the surroundings, or is in the process of being discharged, thereby rendering it impossible to recycle the gas, should such prove desirable.
Thus, there is a demand for a method by which the sulphur trioxide content of a dry exhaust gas can be measured downstream of an absorption tower in a sulphuric acid plant, so that the gas can be checked and controlled in a rapid fashion.